Many semiconductor devices are sensitive to contamination, humidity, and other such environmental factors. To protect them from harm, the devices must be put in a hermetically sealed package. In the past, a device had to first be cut or otherwise separated from its wafer before it could be put into a package. In wafer-level packaging, packaging is performed while the device remains on the wafer. In this fashion, hundreds or thousands of packages can be created simultaneously, and then separated by sawing or other means.
FIG. 1 illustrates an exemplary wafer-level package 101. A first wafer 102 has a gasket 103 bonded to a second wafer 107, creating a hermetically sealed environment 109 between the two wafers to protect a device 111. Only a portion of wafer 102 and wafer 107 are shown in the figure, but there can be hundreds or thousands of such wafer-level packages formed simultaneously between the two wafers. The gasket 103 is created by depositing material such as metal or a polyimide onto wafer 102 in the desired gasket shape. The two wafers are then bonded together at the gasket. This method is effective in creating hermetically sealed environment 109. However, the deposited material is not very rigid, and is prone to deformation when pressure is applied during the bonding process. Since much of the applied pressure is used up by gasket deformation, very little of the applied pressure actually transfers to the bond juncture itself. Therefore, more pressure has to be applied for a longer period of time to create the bond. Furthermore, the process of depositing material creates an irregular gasket bonding surface, which causes problems during bonding. Finally, it is difficult to precisely control the geometry of the gasket, since the deposited material tends to shrink or change shape during the deposition process.